The softening point is defined as the temperature at which a bitumen sample can no longer support the weight of a 3.5-g steel ball. Although it is commonly used in Europe, it is mostly used for roofing asphalts in the U.S. Basically, two horizontal disks of bitumen, cast in shouldered brass rings (Figure 1), are heated at a controlled rate in a liquid bath while each supports a steel ball. The softening point is reported as the mean of the temperatures at which the two disks soften enough to allow each ball, enveloped in bitumen, to fall a distance of 25 mm (1.0 inch) (AASHTO, 2000).
Standard Test Methods
- AASHTO T 53 and ASTM D 36: Softening Point of Bitumen (Ring-and-Ball Apparatus)